1. Background of the Invention
A short axis oscillating probe is known as a probe that electronically scans a piezoelectric element group in the short axis direction thereof, and mechanically scans (oscillates) in the short axis direction thereof to obtain a three dimensional image of an examination subject (refer to Japanese Examined Patent Publication No. Hei 7-38851, Japanese Unexamined Patent Publication No. 2003-175033, Japanese Patent Application No. 2005-175700, and Japanese Unexamined Patent Publication No. 2005-334107 (FIG. 3, FIG. 5)). Consequently, such a probe has been brought to practical application because for example wiring (electrical connection) and scanning circuits thereof, can be made simpler, compared for example to a matrix type probe in which piezoelectric elements are arranged in lengthwise and crosswise array to be electronically scanned in a two-dimensional direction.
2. Prior Art
FIG. 3 is a drawing for explaining a conventional example of a short axis oscillating probe, wherein FIG. 3A is a sectional view in the long axis direction of a piezoelectric element group, and FIG. 3B is a sectional view in the short axis direction. The short axis oscillating probe is such that a piezoelectric element group 102 provided on a rotational retention base 101 is housed within a sealed container 103. The rotational retention base 101 is of a sectionally channel shape with leg sections 101a and 101b on both end sides of a horizontal section thereof, and on the horizontal section of the rotational retention base 101, there is arranged the piezoelectric element group 102. Moreover, on the inner side face of one of the leg sections 101b there is fixed a first bevel gear 104a. 
The piezoelectric element group 102 is configured such that a large number of piezoelectric elements 102a are arranged in the long axis direction. Here it is fastened onto a backing member 105a on a curve-surfaced base 105 provided on the horizontal section of the rotational retention base 101. As a result, the ultrasonic probe is made as a so called convex type. On the surface of the piezoelectric element group 102, generally there is provided an acoustic matching layer 106c that brings acoustic impedance close to that of a living body (human body) to increase propagation efficiency, and on the top face of the acoustic matching layer 106c there is further provided an acoustic lens 106.
The sealed container 103 is joined by fitting together a container main body 103a and a cover 103b, the cross-sections of which are both concave shaped. On a pair of opposing side walls of the container main body 103a, there is provided a pair of rotational center shafts 7 that rotate and oscillate the rotational retention base 101 (the piezoelectric element group 102) in the short axis direction, and the rotational shafts 107 slidably engage with bearings 107a of the leg sections 101a and 101b on both end sides of the rotational retention base 101. A rotational shaft 108 connected to a rotating mechanism such as motor passes in a sealed condition through a bottom wall of the container main body 103a, and on the tip end of the rotational shaft 108 there is provided a second bevel gear 104b so as to mesh with the first bevel gear 104a. 
The inside of the sealed container 103 is filled with a liquid that serves as an ultrasonic wave medium such as oil L that results in bringing the acoustic impedance close to that of a human body and with a low ultrasonic wave propagation loss. Accordingly, ultrasonic wave propagation loss between the inner circumferential surface of the cover 103b and the piezoelectric element group 102 (acoustic lens 106) becomes lower, and the acoustic impedance matching with a human body can be increased. Consequently ultrasonic wave propagation efficiency is increased. If air is present between the inner circumferential surface of the cover 103b and the surface of the piezoelectric element group 102, attenuation of the ultrasonic waves becomes significant and propagation efficiency becomes degraded. As a result, it is not possible to perform excellent transmission/reception of ultrasonic waves.
The oil L is filled from an inlet hole 110 provided in the bottom face of the container main body 103a. When injecting the oil L, the bottom face of the container main body 103 is faced upwards and the pre-degassed oil L is injected. Then, for example, a sealing ring (O ring) (not shown) is attached to the inlet hole 110, and the container main body 103 is sealed with a sealing lid 111a having a male thread.
A rotating mechanism 110 such as motor is covered by a back side surface cover 119, and a cable 118 to be connected to a diagnostic tool is led out from the back side surface cover 119. As a result, rotation of the second bevel gear 104b rotates and oscillates the first bevel gear 104a in the short axis direction, and the rotational retention base 101 (piezoelectric element group 102) integrated with this rotates and oscillates left and right about the center line that equally divides the short axis direction.